linux-kernel - Performance impact of CONFIG_SCHED

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Message-ID: <20100805205448.GB6318@comet.dominikbrodowski.net>
Date:	Thu, 5 Aug 2010 22:54:48 +0200
From:	Dominik Brodowski <linux@...inikbrodowski.net>
To:	linux-kernel@...r.kernel.org, mingo@...hat.com,
	peterz@...radead.org
Cc:	Chris Mason <chris.mason@...cle.com>, josef@...hat.com,
	Valdis.Kletnieks@...edu,
	Michael Monnerie <michael.monnerie@...it-management.at>,
	Christoph Hellwig <hch@...radead.org>,
	linux-raid@...r.kernel.org, xfs@....sgi.com, dm-devel@...hat.com
Subject: Performance impact of CONFIG_SCHED_MC? direct-io test case

How large is the performance impact of CONFIG_SCHED_MC -- for which there
is a warning that it comes "at a cost of slightly increased overhead in
some places."? Well, for the test workload I've been working with lately,

dd if=<device> of=/dev/zero bs=8k count=100000 iflag=direct

where <device> is a dm-crypted LVM volume consisting of several
partitions on a notebook pata harddisk, and all this runs on a Core2 Duo,
I get a ~ 10 % performance reduction if CONFIG_SCHED_MC is enabled.

Combined with the CONFIG_DEBUG performance reduction mentioned in the other
message, all of the reduction from 28 MB/s to 18 MB/s is explained for.

Best,
	Dominik

PS: Ingo: you got both mingo@...e.hu and mingo@...hat.com in MAINTAINERS,
I suppose both are valid?
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